In wafer manufacture probing is a process for testing if dies formed on a wafer are functional. Probing dies on a wafer involves penetrating the surface of the wafer at predetermined points to make contact with the pads of each die. The probe uses probe needles to make contact with the pads of each die. Once the probe has penetrated the surface of the die an electronic signal is passed through the die from at least one probe needle to at least one other probe needle. Information received from the probe needle(s) is used to determine the functionality of the die.
Problems may arise in the probing process due to a number of different reasons. These reasons include dirt being trapped on the probing needles, surface residue building up on the probing needles, and the probing needles becoming bent out of shape.
There are two types of dirt that affect probe needles, gradual material build-up on the needles and sudden dirt build-up. The gradual build-up occurs over a period of time of prolonged usage of the probe card. This build-up may include oxide and pad residue that remain on the probe card after scrubbing. This build-up gradually increases the resistance of the needle in a stable manner. The resistance is not easily noticeable.
The second type of build-up is the sudden build-up. This occurs when a probe needle picks up dirt during the testing process. Sudden dirt build-up leads to an increase in resistance of the needle. Sudden dirt build-up may be caused by foreign particles such as dust, fibre and other airborne particles.
At present probe needles are cleaned after testing a set number of die for example 50. If the number of dies between needle cleaning is too great then a number of good die may fail the probing process due to dirty probe needles. For example in the 50 die cleaning interval could mean that 49 dies are tested by a probe with dirty probe needles before the dust is cleaned away. If the number of die between needle cleanings is too low then the needles may be cleaned excessively leading to a slower testing process and more wear and tear on the needles. The present cleaning regime is ineffective against sudden build-up, which may lead to a large number of good dies failing the probing test.